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Research Papers

A Longitudinal Study of Remodeling in a Revised Peripheral Artery Bypass Graft Using 3D Ultrasound Imaging and Computational Hemodynamics

[+] Author and Article Information
Patrick M. McGah1

Department of Mechanical Engineering, University of Washington, Box 352600, Seattle, WA 98195pmcgah@u.washington.edu

Daniel F. Leotta

Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Box 355640, Seattle, WA 98195

Kirk W. Beach

Department of Surgery, Division of Vascular Surgery, University of Washington, Box 356410, Seattle, WA 98195

James J. Riley, Alberto Aliseda

Department of Mechanical Engineering, University of Washington, Box 352600, Seattle, WA 98195

1

Corresponding author.

J Biomech Eng 133(4), 041008 (Mar 23, 2011) (10 pages) doi:10.1115/1.4003622 History: Received August 16, 2010; Revised January 28, 2011; Posted February 09, 2011; Published March 23, 2011; Online March 23, 2011

We report a study of the role of hemodynamic shear stress in the remodeling and failure of a peripheral artery bypass graft. Three separate scans of a femoral to popliteal above-knee bypass graft were taken over the course of a 16 month period following a revision of the graft. The morphology of the lumen is reconstructed from data obtained by a custom 3D ultrasound system. Numerical simulations are performed with the patient-specific geometries and physiologically realistic flow rates. The ultrasound reconstructions reveal two significant areas of remodeling: a stenosis with over 85% reduction in area, which ultimately caused graft failure, and a poststenotic dilatation or widening of the lumen. Likewise, the simulations reveal a complicated hemodynamic environment within the graft. Preliminary comparisons with in vivo velocimetry also showed qualitative agreement with the flow dynamics observed in the simulations. Two distinct flow features are discerned and are hypothesized to directly initiate the observed in vivo remodeling. First, a flow separation occurs at the stenosis. A low shear recirculation region subsequently develops distal to the stenosis. The low shear region is thought to be conducive to smooth muscle cell proliferation and intimal growth. A poststenotic jet issues from the stenosis and subsequently impinges onto the lumen wall. The lumen dilation is thought to be a direct result of the high shear stress and high frequency pressure fluctuations associated with the jet impingement.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Surface reconstructions of the three acquired bypass graft images registered in a common coordinate system. Reconstructions are chronological from top to bottom. Times of acquisition are 1 month, 6 months, and 16 months after a PTFE patch angioplasty. The distal patch anastomosis is used as the fiducial marker. The patch is approximately located between x=−30 mm and x=+10 mm on the top part of the reconstruction and covers about one-third of the vessel circumference.

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Figure 2

Cross-sectional area measurements versus graft axis for three surface reconstructions. Coordinate system is the same as that in Fig. 1.

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Figure 3

Idealized volumetric flow rate applied at domain inlet (in ml/min) versus time. The time has been normalized with the period. The same waveform is used for the simulations in all three graft scans.

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Figure 4

Instantaneous streamwise velocity contours of the 1 month scan at time t/T=1. Top subfigure is a 3D depiction of the surface of constant x-velocity (0.15 m/s). (a)–(c) depict the out-of-plane velocity contours at three axial slices located at x=−27, −17, and −2 mm, respectively. Bar labeled 3 mm gives relative size of the three subfigures.

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Figure 5

Instantaneous streamwise velocity contours of the 6 month scan at time t/T=1. Top subfigure is a 3D depiction of the surface of constant x-velocity (0.15 m/s). (a)–(c) depict the out-of-plane velocity contours at three axial slices located at x=−27, −17, and −2 mm, respectively. Bar labeled 3 mm gives relative size of the three subfigures.

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Figure 6

Instantaneous streamwise velocity contours on a 2D plane of the 1 month scan at time t/T=1 detailing the flow separation and recirculation zone. Dark line delineates forward moving versus reversed flow. The Z (out-of-plane) position of the plane is in the approximate vessel center.

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Figure 7

Time-averaged wall shear stress contours on graft lumen for one cycle (in Pa). Scans are chronological from top to bottom and the flow is from left to right. WSS is approximately symmetrical on the backside of the lumen.

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Figure 8

OSI contours on graft lumen for one cycle. Scans are chronological from top to bottom and the flow is from left to right. OSI is approximately symmetrical on the backside of the lumen.

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Figure 9

WSSG contours on graft lumen averaged over one cycle (in Pa/m). Scans are chronological from top to bottom and the flow is from left to right. WSSG is approximately symmetrical on the backside of the lumen.

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Figure 10

Visualization of the velocity in the poststenotic jet in the 16 month scan. The time is t/T=1 at the end of the fifth cycle. (a) Instantaneous streamwise velocity isosurface (=0.50 m/s). The dots indicate the points used to measure the time histories depicted in Fig. 1 (left dot) and Fig. 1 (right dot). (b) Coherent vortices identified by the Q criterion. Q value is 0.3 (normalized with stenosis diameter and mean stenosis centerline velocity).

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Figure 11

Phase-averaged x-velocity history at two spatial points in the 16 month scan; (a) is at a point located near the stenosis throat and (b) is located in the mid-dilated region. See the dots in Fig. 1 for specific locations.

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Figure 12

Streamwise velocity power spectrum versus frequency. The velocity signal is from the 16 month scan in the poststenotic region and at the same point as given in Fig. 1. The frequency spectrum is computed from the five simulated cycles. Note the spectral energy at frequencies <10 Hz, indicating the cardiac cycle frequencies, and the energy at 100–500 Hz, indicating the jet transition.

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Figure 13

In vivo Doppler ultrasound measurements of velocity at the stenosis throat for one cardiac cycle. Abscissa is the time (approximately 1 s) and ordinate is the velocity (cm/s). Compare with Fig. 1.

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Figure 14

In vivo Doppler ultrasound measurements of velocity near the distal graft anastomosis for one cardiac cycle. Abscissa is the time (approximately 1 s) and ordinate is the velocity (cm/s). Compare with Fig. 1.

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Figure 15

Streamwise velocity versus time for one simulated cardiac cycle. Point is near the distal graft anastomosis (x≈5 mm) in the center of the vessel. Compare with Fig. 1.

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Figure 16

Time-averaged WSS (in Pa) on the graft lumen for the scan at 1 month. The perspective has been rotated 90 deg counterclockwise about the x-axis compared with that in Fig. 7. Black color represents TAWSS<0.2 Pa, dark gray color represents 0.2 Pa<TAWSS<0.5 Pa, and light gray color represents TAWSS>0.5 Pa. The arrow indicates the future location of the stenosis (x≈−27 mm).

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